Photoresist, compounds for composing the photoresist, and method of forming pattern by using the photoresist

ABSTRACT

There is provided a photoresist including (a) a resin composed of a polymer represented with the following general formula [1], and (b) a photo acid generator which produces acid when exposed to a light: ##STR1## wherein each of R 1 , R 3  and R 7  represents one of a hydrogen atom and a methyl group, R 2  represents a hydrocarbon group including a bridged cyclic hydrocarbon group and having a carbon number in the range of 7 to 13 both inclusive, R 4  represents one of a hydrogen atom and a hydrocarbon group having a carbon number of 1 or 2, R 5  represents a hydrocarbon group having a carbon number of 1 or 2, R 6  represents one of (a) a hydrocarbon group having a carbon number in the range of 1 to 12 both inclusive, (b) a hydrocarbon group having a carbon number in the range of 1 to 12 both inclusive and replaced with an alkoxy group having a carbon number in the range of 1 to 12 both inclusive, and (c) a hydrocarbon group having a carbon number in the range of 1 to 12 both inclusive and replaced with an acyl group having a carbon number in the range of 1 to 13 both inclusive, x+y+z=1, x is in the range of 0.1 to 0.9, y is in the range of 0.1 to 0.7, and z is in the range of 0 to 0.7. The resin has a weight percent in the range of 75 to 99.8 both inclusive, and the photo acid generator has a weight percent in the range of 0.2 to 25 both inclusive. The above mentioned photoresist produces no extra polymer by side reaction. Thus, the photoresist has high resolution to thereby make it possible to form a fine pattern without resist residue.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a photoresist and compounds of whichthe photoresist is made, and further relates to a method of forming aresist pattern by using the photoresist.

2. Description of the Related Art

In a field of manufacturing various electronic devices such as VLSI inwhich sub-micron order patterns are required to form, an electric deviceis now required to have higher densification and integration. Thus, animproved lithography technique for forming a more minute pattern on asubstrate is required for satisfying such a requirement.

As one of methods for forming a more minute pattern is known a method inwhich an exposure light having a shorter wavelength is used for forminga resist pattern. For instance, there has been used i-line ofhigh-pressure mercury vapor lamp, which has a wave length of 365 nm, asa light source for forming a dynamic random access memory (DRAM) havingan integration of 64 M bits or less. In a mass production of a 0.25μm-rule 256 M bits DRAM, it is now being expected that the i-line isreplaced with KrF excimer laser, as an exposure light source, having ashorter wavelength than that of the i-line, more specifically, having awavelength of 248 nm. However, the fabrication of 0.18 μm-rule 1 G bitsor greater DRAM which requires a technique for forming a more finepatterns needs a light source having a shorter wavelength than that ofKrF excimer laser to be developed. For that purpose, an ArF excimerlaser having a wavelength of 193 nm now attracts attention as a lightsource to be used in photolithography. For instance, the utilization ofArF excimer laser is discussed by T. Ueno, T. Iwayanagi, K. Nono, H. Itoand C. Grant Willson: "Resist Materials for Short Wavelength" BunshinShuppan Inc., 1988.

Hence, there is now expected to develop a new resist to be employed forphotolithography in which ArF excimer laser is to be used. Such a resistused for ArF light exposure is required to enhance cost performance oflaser, because a gas from which laser is radiated has short life-time,and also because a laser radiating equipment is expensive. Thus, theresist is expected to have a high resolution as well as a highsensitivity in response to a design rule getting smaller and smaller.

As one of methods of enhancing a sensitivity of resist, there has beenwell known a chemically amplified resist which utilizes a photo acidgenerator as a sensitizer. For typical instance, Japanese PatentPublication No. 2-27660 has suggested a resist comprised of acombination of triphenylsulfonium hexafluoroarsenate and poly(p-tert-butoxycarbonyloxy-α-methylstyrene). There are many reports abouta chemically amplified resist for use with a KrF excimer laser, forinstance, one of which is American Chemical Society Symposium Series,1984, Vol. 242, pages 11-23, reported by Hiroshi Ito and C. GrantWillson. A chemically amplified resist is characterized by the steps ofgenerating proton acid by exposing a photo acid generator to a light,and transferring the thus generated proton acid through a resist solidphase by means of post-exposure heat treatment to thereby amplifychemical reaction of the resist resin up to hundreds of to thousands oftimes due to the proton acid in a way like catalytic action. Thus, aquite higher sensitivity can be attained relative to a prior resistwhich has an optical reaction efficiency, which is defined as a reactionper a photon, of smaller than one (1).

Presently, most of newly developed resists are chemically amplifiedresists, and hence a chemical amplification system has to be adopted indevelopment of a high sensitive material in response to a wavelength ofan exposure light source getting smaller and smaller.

In a conventional lithography in which there is employed an exposurelight having a longer wavelength than that of KrF excimer laser having awavelength of 248 nm, a photoresist contains a resin having aromaticrings in a structural unit, such as novolac resin and poly(p-vinylphenol). The dry etching resistance of such aromatic rings givesa dry etching resistance to the above mentioned resin.

However, the aromatic rings quite intensively absorb lights having awavelength equal to or shorter than 220 nm such as ArF excimer laserhaving a wavelength of 193 nm, and hence the above mentionedconventional resins cannot be applied to a photolithography in whichthere is used a light source emitting deep ultraviolet radiation (DUV)having a wavelength equal to or shorter than 220 nm. Thus, there is nowstudied a resin which does not contain aromatic rings, but has etchingresistance, and which contains alicyclic hydrocarbon. For instance, sucha resin has been reported by S. Takechi, Journal of Photopolymer Scienceand Technology, Vol. 5, No. 3, 1992, pp. 439-446.

However, since alicyclic groups have strong hydrophobic property, theintroduction of alicyclic groups causes a resin containing the alicyclicgroups to have stronger hydrophobic property, which would cause problemsthat adhesion of a formed thin film to a silicon substrate isdeteriorated, and that the uniformity of a thickness of a film to beformed on a substrate is also deteriorated.

As one of solutions to the problems, there has been suggested the use ofmethacrylic acid unit. For instance, the inventors have alreadysuggested the copolymer in "Positive Chemically Amplified Resist for ArFExcimer Laser Lithography Composed of a Novel Transparent PhotoacidGenerator and an Alicyclic Terpolymer", Proceeding of SPIE, Vol. 2438,1995, pp. 433-444. The copolymer consists of tricyclodecanylacrylate,tetrahydropyranylmethacrylate and methacrylic acid, and is a resin usedfor a resist into which alicyclic groups and methacrylic acid units areintroduced.

Thus, a polymer having transparency to a light having a wavelength of193 nm and also having a dry-etching resistance can be attained byintroduction of alicyclic polymers, and the above mentioned problems ofdeterioration in adhesion and film thickness uniformity which would becaused by the introduction of alicyclic polymers can be overcome byintroduction of methacrylic acid units. The above mentioned resin forcomposing a resist generally includes tetrahydropyranyl groups andtert-butyl groups as a protective group which is decomposed by acid andchanges a polarity of a polymer. For instance, the use of atetrahydropyranyl group has been reported in K. Nakano, K. Maeda, S.Iwasa, T. Ohfuji and E. Hasegawa: "Positive Chemically Amplified Resistfor ArF Excimer Laser Lithography Composed of a Novel TransparentPhotoacid Generator and an Alicyclic Terpolymer", Proceeding of SPIE,Vol. 2438, pp.433-444, and the use of a tert-butyl group has beenreported in R. D. Allen, G. M. Wallraff, R. A. Dipietro, D. C. Hofer andR. R. Kunz: "Single Layer Resists with Enhanced Etch Resistance for 193nm Lithography", Journal of Photopolymer Science and Technology, Vol. 7,No. 3, 1994, pp. 507-516.

However, a tetrahydropyranyl group has shortcomings of a low thermaldecomposition point and low thermal stability. In addition, it is knownthat a tetrahydropyranyl group produces a polymer as a result of sidereaction, when used as a protective group for polyvinylphenol, asreported in T. Sakamizu, H. Shiraishi, H. Yamaguchi, T. Ueno and N.Hayashi: "Acid-Catalyzed Reactions of Tetrahydropyranyl-ProtectedPolyvinylphenol in a Novolak-Resin-Based Positive Resist", JapaneseJournal Application Physics, Vol. 31, 1992, pp. 4288-4293.

Similarly, when a tetrahydropyranyl group is used as a protective groupfor methacrylic acid, there will be formed a polymer as a result of sidereaction in a way as shown in the following chemical reaction formula[5]. Namely, a tetrahydropyranyl group has faults as a protective groupthat it will produce a polymer as a by-product which prevents the resistfrom being dissolved to a developing agent to thereby deteriorateresolution of the resist, and further thereby produce resist residue orscum. ##STR2##

On the other hand, a tert-butyl group does not proceed desorptionquantitatively unless a strong acid such as triphlate acid is used.Hence, a photo acid generator to be used in the photoresist is limitedto one which would produce triphlate acid, such astriphenylsulfoniumtrifluoromethanesulfonate. However, triphlate acid hashigh volatility, and tends to be evapotraspired from a resist filmbefore a resist is developed. In addition, as triphlate acid is a strongacid, it readily reacts with basic compounds existing in the air. Thus,there tends to be produced a so-called surface dissolution resistinglayer on which, when triphlate acid is used, triphlate acid isdeactivated and thus cannot reach an effective amount at a part of asurface of a resist film, and hence a pattern on the part cannotresolved. As a result, the resolution of a resist is remarkablydeteriorated. The study about this phenomenon is provided by S. A.MacDonald et al., Proceedings of SPIE, 1991, Vol. 1446, pp. 2-12.

As discussed above, a resist for lithography employing a light having awavelength equal to or smaller than 220 nm has the etching resistanceand adhesion to a substrate, but does not have protective groups forchanging polarity of a resin. Thus, there has been suggested no resistshaving high resolution and high sensitivity by which a fine pattern canbe obtained without production of scum.

SUMMARY OF THE INVENTION

In view of the shortcomings of prior photoresists, it is an object ofthe present invention to provide a photoresist to be used in lithographyin which there is employed a light source emitting far ultravioletradiation having a wavelength equal to or smaller than 220 nm, such asArF excimer laser, which photoresist provides high resolution and highthermal stability.

It is also an object of the present invention to provide a polymer ofwhich the above mentioned photoresist is made.

It is another object of the present invention to provide a method ofpatterning a photoresist, which method makes it possible to form a fineresist pattern.

The inventors have studied a protective group which has higher thermalstability than a tetrahydropyranyl group, which is not accompanied withside reaction, and which is decomposable in acid. As a result of thelong term study, the inventors could reach the inventions mentionedhereinbelow by which all of the above mentioned problems can beovercome.

In one aspect, there is provided a polymer represented with thefollowing general formula [1]: ##STR3##

wherein each of R¹, R³ and R⁷ represents one of a hydrogen atom and aethyl group, R² represents a hydrocarbon group including a bridgedcyclic hydrocarbon group and having a carbon number in the range of 7 to13 both inclusive, R⁴ represents one of a hydrogen atom and ahydrocarbon group having a carbon number of 1 or 2, R⁵ represents ahydrocarbon group having a carbon number of 1 or 2, R⁶ represents one of(a) a hydrocarbon group having a carbon number in the range of 1 to 12both inclusive, (b) a hydrocarbon group having a carbon number in therange of 1 to 12 both inclusive and replaced with an alkoxy group havinga carbon number in the range of 1 to 12 both inclusive, and (c) ahydrocarbon group having a carbon number in the range of 1 to 12 bothinclusive and replaced with an acyl group having a carbon number in therange of 1 to 13 both inclusive, x+y+z=1, x is in the range of 0.1 to0.9, y is in the range of 0.1 to 0.7, and z is in the range of 0 to 0.7.

It is preferable that the above mentioned polymer has a weight averagemolecular weight in the range of 1,000 to 1,000,000 both inclusive.

In another aspect, there is provided a photoresist including (a) a resincomposed of a polymer represented with the above mentioned generalformula [1], and (b) a photo acid generator which produces acid whenexposed to a light. The resin has a weight percent in the range of 75 to99.8 both inclusive, and the photo acid generator has a weight percentin the range of 0.2 to 25 both inclusive.

The hydrocarbon group represented with R² includes, for instance, atricyclo [5.2.1.0²,6 ] decyl group, a tetracyclo [4.4.0.1²,5.1⁷,10 ]dodecyl group, a dicyclopentenyl group, a dicyclopentenyloxyethyl group,a norbonyl group and an adamantyl group. However, the divalenthydrocarbon group R² is not to be limited to those listed above.

Each of the hydrocarbon groups represented with R⁴ and R⁵ is, forinstance, a methyl group or an ethyl group.

The hydrocarbon group represented with R⁶ includes, for instance, amethyl group, an ethyl group, a propyl group, a butyl group, a pentylgroup, a hexyl group, a heptyl group, an octyl group, a nonyl group, adecyl group, an undecyl group, a dodecyl group, a cyclopentyl group, acyclohexyl group, a cycloheptyl group, a norbornyl group, atricyclodecyl group, a dicyclopentenyl group, a cyclohexyl group, anorbonyl group, an adamantyl group, a methoxyethyl group, an ethoxyethylgroup, a propoxyethyl group, a butoxyethyl group, a pentyloxyethylgroup, a hexyloxyethyl group, a heptyloxyethyl group, acycloheptyloxyethyl group, a cyclohexyloxyethyl group, acyclopentyloxyethyl group, a cyclohexyloxyethyl group, acyclooctyloxyethyl group, a norbornyloxyethyl group, anadamantyloxyethyl group, a methoxypropyl group, an ethoxypropyl group, apropoxypropyl group, an acetoxyethyl group, and anadamantylcarbonyloxyethyl group. However, the hydrocarbon group R⁶ isnot to be limited to those listed above.

The above mentioned polymer in accordance with the present invention canovercome the earlier discussed problems. In a resin containing thepolymer defined by the general formula [1], a part represented with thefollowing general formula [2] is easily decomposed by acid to therebychange polarity of the polymer. The part represented with the generalformula [2] is decomposed by heated acid into carboxylic acid, alcoholand aldehyde. ##STR4##

In the general formula [2], each of the hydrocarbon groups representedwith R⁴ and R⁵ is, for instance, a methyl group or an ethyl group, andR⁶ represents one of (a) a hydrocarbon group having a carbon number inthe range of 1 to 12 both inclusive, (b) a hydrocarbon group having acarbon number in the range of 1 to 12 both inclusive and replaced withan alkoxy group having a carbon number in the range of 1 to 12 bothinclusive, and (c) a hydrocarbon group having a carbon number in therange of 1 to 12 both inclusive and replaced with an acyl group having acarbon number in the range of 1 to 13 both inclusive.

The hydrocarbon group represented with R⁶ includes, for instance, amethyl group, an ethyl group, a propyl group, a butyl group, a pentylgroup, a hexyl group, a heptyl group, an octyl group, a nonyl group, adecyl group, an undecyl group, a dodecyl group, a cyclopentyl group, acyclohexyl group, a cycloheptyl group, a norbornyl group, atricyclodecanyl group, a dicyclopentenyl group, a cyclohexyl group, anorbonyl group, an adamantyl group, a methoxyethyl group, an ethoxyethylgroup, a propoxyethyl group, a butoxyethyl group, a pentyloxyethylgroup, a hexyloxyethyl group, a heptyloxyethyl group, acycloheptyloxyethyl group, a cyclohexyloxyethyl group, acyclopentyloxyethyl group, a cyclohexyloxyethyl group, acyclooctyloxyethyl group, a norbornyloxyethyl group, anadamantyloxyethyl group, a methoxypropyl group, an ethoxypropyl group, apropoxypropyl group, an acetoxyethyl group, and anadamantylcarbonyloxyethyl group. However, the hydrocarbon group R⁶ isnot to be limited to those listed above.

Since the part represented with the general formula [2] has alkoxygroups which are one of electron donating groups, and have small sterichindrance to acid, acid is readily accessible to the part. Thus,decomposition proceeds more rapidly than conventionally usedtetrahydropyranyl group and tert-butyl group. Accordingly, a photoresistmade of the polymers in accordance with the present invention makes itpossible to carry out resolution with smaller amount of light forexposure than a conventional resin to be used for ArF excimer laserlithography employing a tert-butyl group or a tetrahydropyranyl group.

A tert-butyl group has low desorption reaction efficiency, and hencecould not carry out resolution unless there is used a photo acidgenerator which produces strong acid such as triphlate acid. However, ifa photo acid generator which will produce strong acid such as triphlateacid is employed, a photoresist tends to be influenced by the effect ofunlikeliness of dissolution of a surface thereof, and hence it isdifficult to form a fine pattern. Thus, a surface protection film needsto be formed over a resist.

On the other hand, the photoresist made in accordance with the presentinvention makes it possible to carry out resolution, even if there isemployed a photo acid generator which produces weaker acid thantriphlate acid, such as toluenesulfonic acid. In addition, thephotoresist made in accordance with the present invention produces noany polymers as by-products unlike a conventional resin employing atetrahydropyranyl group therein. Thus, the present invention makes itpossible to form a fine resist pattern without resist residue or scum.

In still another aspect, there is provided a method of patterning aphotoresist, including the steps of (a) applying a photoresist on asubstrate, (b) exposing the photoresist to a light having a wavelengthsmaller than 400 nanometers, and (c) developing the photoresist tothereby form a resist pattern. Herein, the photoresist includes (a) aresin composed of a polymer represented with the above mentioned generalformula [1], and (b) a photo acid generator which produces acid whenexposed to a light. The resin has a weight percent in the range of 75 to99.8 both inclusive, and the photo acid generator has a weight percentin the range of 0.2 to 25 both inclusive.

It is preferable that the light has a wavelength in the range of 180nanometers to 220 nanometers. It is also preferable that there isemployed ArF excimer laser as the light.

It is preferable that the photo acid generator as a constituent of thephotoresist made in accordance with the present invention is one thatgenerates an acid when exposed to a light which preferably has awavelength equal to or less than 400 nm, more preferably in the range of180 to 220 nm both inclusive. Any photo acid generator may be used forthe present invention, if a mixture of the earlier mentioned polymermade in accordance with the invention and the photo acid generator issufficiently soluble in an organic solvent, and further if it ispossible to form a uniform deposition film from the solution by means ofa layer forming process such as a spin coating process. One or morephoto acid generators may be mixed for use with the invention. As analternative, the photo acid generator may be used in combination withappropriate photosensitizer(s).

Photo acid generators usable for reducing the present invention intopractice may be selected, for instance, from any one of (a)triphenylsulfonium salt derivatives proposed in Journal of the OrganicChemistry, 1978, Vol. 43, No. 15, pp. 3055-3058, by J. V. Crivello etal., (b) onium salts such as sulfonium salt, iodonium salt, phosphoniumsalt, diazonium salt and ammonium salt, (c) 2,6-dinitrobenzyl esterproposed in Proceedings of SPIE, 1989, Vol. 1086, pp. 2-10, by T. Neenanet al., (d), 1, 2, 3-tri (methanesulfonyloxy) benzene proposed inProceedings of PME '89, 1990, pp 413-424, by Takumi Ueno et al.,published through Kodansha, (e) sulfosuccinimide disclosed in JapaneseUnexamined Patent Publication No. 5-134416. However, it should be notedthat a photo acid generator to be used for the present invention is notto be limited to the above mentioned ones (a) to (e).

The most preferable photo acid generators are ones represented with thefollowing general formulas [3] and [4]. ##STR5##

In the formula [3], each of R⁷ and R⁸ represents one of straight-chain,branch-type and cyclic alkyl groups, and R⁹ represents one of (a) astraight-chain, branch-type or cyclic alkyl group, (b) a 2-oxo cyclicalkyl group, (c) a 2-oxo straight-chain alkyl group, and (d) a 2-oxobranch-type alkyl group, and Y⁻ is a negative ion in the pair shown andmay represent negative ions such as BF₄ --, AsF₆ --, SbF₆ --, PF₆ --,CF₃ COO--, ClO₄ --, and CF₃ SO₃ --. ##STR6##

In the formula [4], R¹⁰ represents one of (a) a straight-chain,branch-type or cyclic alkyl group, (b) a replaced aromatic ring, and (c)a non-replaced aromatic ring, and each of R¹¹ and R¹² represents one of(a) a straight-chain, branch-type or cyclic alkyl group and (b) astraight-chain, branch-type or cyclic haloalkyl group.

A photo acid generator presently, widely used for KrF excimer laserlithography, such as triphenylsulfonium trifluoromethanesulfonate(hereinafter, referred to simply as "TPS"), has a quite stronglight-absorbing property for deep ultraviolet radiation (DUV) having awavelength equal to or smaller than 220 nm, and hence it is required tolimit an amount thereof, if it is to be used as a photo acid generatorin the present invention. Now comparing a transmissivity at a wavelengthof 193.4 nm which is a main wavelength of ArF excimer laser beam, atransmissivity of a deposition film having a thickness of 1 μm andcomposed of polymethylmethacrylate containing TPS at 1.5 wt % on thebasis of a total weight of the film was about 50%, and a transmissivityof a film having a thickness of 1 μm and composed ofpolymethylmethacrylate containing TPS at 5. 5 wt % was about 6%. On theother hand, a transmissivity of a polymethylmethacrylate deposition filmcontaining therein, for instance,cyclohexylmethyl(2-oxocyclohexyl)sulfoniumtrifluoromethanesulfonate,which is one of sulfonium salt derivatives represented with the generalformula [3], was 71% when the film contained the above mentionedcompound at 5 wt %, and was 55% at 30 wt %, both of which are higherthan the formerly mentioned transmissivity. A transmissivity of adeposition film containing therein, for instance,N-hydroxysuccinimidetrifluoromethanesulfonate, which is one of photoacid generators represented with the general formula [4], was about 50%,when the film contained the above mentioned compound at 5 wt %.

As discussed above, any of the photo acid generators represented withthe general formulas [3] and [4] absorbs quite little amount of light inthe band of DUV having a wavelength ranging from 180 nm to 220 nm, andaccordingly it is obvious that they are preferable for a constituent ofa resist to be used for ArF excimer laser lithography in terms oftransparency to an exposure light. Specifically, a photo acid generatorto be used for the photoresist made in accordance with the presentinvention may be selected from any one of

(a)2-oxocyclohexylmethyl(2-norbornyl)sulfoniumtrifluoromethanesulfonate,

(b) cyclohexylmethyl(2-oxocyclohexyl)sulfoniumtrifluoromethanesulfonate,

(c) dicyclohexyl(2-oxocyclohexyl)sulfoniumtrifluoromethanesufonate,

(d) dicyclohexylsulfonylcyclohexanone,

(e) dimethyl(2-oxocyclohexyl)sulfoniumtrifluoromethanesulfonate,

(f) triphenylsulfoniumtrifluoromethanesulfonate,

(g) diphenyliodoniumtrifluoromethanesulfonate, and

(h) N-hydroxysuccinimidetrifluoromethanesulfonate.

However, it should be noted that a photo acid generator to be used forthe present invention is not to be limited to those, and any other photoacid generator may be selected.

A single kind of or a plurality of kinds of photo acid generator(s) maybe used in the photoresist made in accordance with the presentinvention. The photo acid generator is contained by weight percentpreferably in the range from 0.2 to 25 both inclusive, and morepreferably in the range from 0.5 to 15 both inclusive, provided that allconstituents containing the photo acid generator constitute 100 wt %. Ifa content rate of the photo acid generator would be lower than 0.2 wt %,the photoresist could have only quite a small sensitivity, and hence theformation of a pattern would become difficult. On the other hand, if acontent rate of the photo acid generator would be higher than 25 wt %,it would be difficult to form a uniform deposition layer, and furtherthere would arise a problem that scum tends to be generated afterdevelopment of a pattern. A content rate of the polymer is preferably inthe range from 75 to 99.8 wt %, and more preferably in the range from 85to 99.5 wt % on the basis of the 100 wt % of all constituents includingthe polymer itself.

Any organic solvent may be used for the photoresist made in accordancewith the present invention, if the polymer and photo acid generatorwould be sufficiently soluble in a solvent, and further if it would bepossible to form a uniform deposition layer from the solution by meansof a method such as a spin coating process. A single kind of solvent ora plurality of kinds of solvents in combination may be used.

Specifically, a solvent to be used for the photoresist made inaccordance with the present invention is selected from any one ofn-propyl alcohol, isopropyl alcohol, n-butyl alcohol, tert-butylalcohol, methylcellosolve acetate, ethylcellosolve acetate,propyleneglycol monoethylether acetate, methyl lactate, ethyl lactate,2-methoxybutyl acetate, 2-ethoxyethyl acetate, pyrubic acid methyl,pyrubic acid ethyl, 3-methoxypropionatemethyl, 3-methoxypropionateethyl,N-methyl-2-pyrrolidinone, cyclohexanone, cyclopentanone, cyclohexanol,methylethylketone, 1,4-dioxan, ethyleneglycolmonomethylether,ethyleneglycolmonomethylether acetate, ethyleneglycolmonoethylether,ethyleneglycolmonoisopropylether, diethyleneglycolmonomethylether, anddiethyleneglycoldimethylether. It should be noted that a solvent to beused for the photoresist is not to be limited to the above mentionedones, but other solvents may be selected.

As would be obvious to those skilled in the art, essential constituentsof the photoresist to be made in accordance with the present inventionare the above mentioned polymer, photo acid generator, and solvent.However, the photoresist may include other constituents such as agentfor preventing dissolution, surfactant, pigment, stabilizer, reagent forenhancing application property, and dye.

As will be obvious in view of the later mentioned preferred embodiments,a resin of which the inventive photoresist is made is thermally, highlystable. In addition, the inventors conducted an experiment forresolution by using ArF excimer laser as an exposure light, andconfirmed that the photoresist in accordance with the present inventionmade it possible to form a rectangular, fine pattern with highsensitivity without resist residue or scum.

That is, the photoresist made in accordance with the present inventionis suitable for the formation of a fine pattern in lithography in whichthere is employed DUV having a wavelength in the range of 180 nm to 220nm as an exposure light.

The above and other objects and advantageous features of the presentinvention will be made apparent from the following description made withreference to the accompanying drawings, in which like referencecharacters designate the same or similar parts throughout the drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1, 2 and 3 are cross-sectional views of a wafer for showing stepsof a method of forming a positive pattern on the wafer by using thephotoresist made in accordance with the present invention.

FIG. 4 is a schematic view illustrating an experimental device forexposing a resist to a light.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments in accordance with the present invention will beexplained hereinbelow.

[SYNTHESIS EXAMPLE 1]

Synthesis of Ethoxyethyl Methacrylate represented with the formula [6]##STR7##

In a flask having four inlets, 15.1 grams (0.21 mols) of ethylvinylehterand 20 grams (0.23 mols) of methacrylic acid were dissolved into 200 mlof methylene chloride. Then, 0.53 grams (0.0021 mols) ofp-toluenesulfonic acid pyridine salt was added to the mixture, andstirred for complete dissolution of p-toluenesulfonic acid pyridine saltinto the mixture. The resultant solution was stood at room temperaturefor six hours. Then, 200 ml of diethylether was added into the solution.The resultant solution was washed three times with 2.5% aqueous sodiumhydroxide, and further six times with water. Then, an ether layer wasdehydrated with magnesium sulfate. After filtering magnesium sulfateout, a methylene chloride layer was evaporated. As a result, there wasobtained 31.8 grams of 1-ethoxyethylmethacrylate. The yield was 96%.With respect to a structure of the target material, IR was measured withan analyzer, IR-470 model available from Shimazu Seisakusho, and ¹ H-NMRwas measured with an analyzer, AMX-400 model available from BrukerInstruments.

IR (liquid film method) (cm⁻¹): 2950, 2880 (ν_(C--H)), 1720 (ν_(C)═O),1640 (ν_(C)═C), 1170 (ν_(C--O))

¹ H-NMR (CDCl₃, internal standard material: tetramethylsilane) ppm:1.15-1.25 (t, 3 H), 1.4-1.5 (w, 3 H), 1.92-1.96 (s, 3 H), 3.4-3.8 (m, 2H), 5.59-5.69 (w, 1 H), 5.98-6 (m, 1 H), 6.15-6.25 (w, 1 H)

[SYNTHESIS EXAMPLE 2]

Synthesis of 1-Butoxyethyl Methacrylate represented with the formula [7]##STR8##

In the same way as the synthesis example 1, synthesis of monomer wasperformed using 21 grams (0.21 mols) of butylvinylether in place ofethylvinylether. As a result, there was obtained 36.6 grams of1-butoxyethyl methacrylate. The yield was 94%.

IR (liquid film method) (cm⁻¹): 2950, 2880 (ν_(C--H)), 1720 (ν_(C)═O),1640 (ν_(C)═C), 1170 (ν_(C--O))

¹ H-NMR (CDCl₃, internal standard material: tetramethylsilane) ppm:0.75-1.85 (m, 10 H), 1.92-1.97 (s, 3 H), 3.42-3.8 (m, 2 H), 5.59-5.69(w, 1 H), 6.00-6.05 (m, 1 H), 6.15-6.25 (w, 1 H)

[SYNTHESIS EXAMPLE 3]

Synthesis of Octyloxyethyl Methacrylate represented with the formula [8]##STR9##

In the same way as the synthesis example 1, synthesis of monomer wasperformed using 32.8 grams (0.21 mols) of octylvinylether in place ofethylvinylether. As a result, there was obtained 46.2 grams ofoctyloxyethyl methacrylate. The yield was 91%.

IR (liquid film method) (cm⁻¹): 2950, 2880 (ν_(C--H)), 1720 (ν_(C)═O),1640 (ν_(C)═C), 1170 (ν_(C--O))

¹ H-NMR (CDCl₃, internal standard material: tetramethylsilane) ppm:0.75-1.85 (m, 18 H), 1.92-1.97 (s, 3 H), 3.42-3.8 (m, 2 H), 5.59-5.69(w, 1 H), 6.00-6.05 (m, 1 H), 6.15-6.25 (w, 1 H)

[SYNTHESIS EXAMPLE 4]

Synthesis of Methoxypropyl Methacrylate represented with the formula [9]##STR10##

In the same way as the synthesis example 1, synthesis of monomer wasperformed using 15.1 grams (0.21 mols) of methylpropenylether in placeof ethylvinylether. As a result, there was obtained 30.5 grams ofmethoxypropyl methacrylate. The yield was 92%.

IR (liquid film method) (cm⁻¹): 2950, 2880 (ν_(C--H)), 1720 (ν_(C)═O),1640 (ν_(C)═C), 1170 (ν_(C--O))

¹ H-NMR (CDCl₃, internal standard material: tetramethylsilane) ppm:1.41-1.5 (s, 6 H), 1.9-1.94 (s, 3 H), 3.47-3.53 (s, 3 H), 5.59-5.69 (w,1 H), 6.15-6.25 (w, 1 H)

[SYNTHESIS EXAMPLE 5]

Synthesis of Methoxyethoxyethyl Methacrylate represented with theformula [10] ##STR11##

In the same way as the synthesis example 1, synthesis of monomer wasperformed using 21.42 grams (0.21 mols) of methoxyethylvinylether inplace of ethylvinylether. As a result, there was obtained 36.3 grams ofmethoxyethoxyethyl methacrylate. The yield was 92%.

IR (liquid film method) (cm⁻¹): 2950, 2880 (ν_(C--H)), 1720 (ν_(C)═O),1640 (ν_(C)═O), 1170 (ν_(C--O))

¹ H-NMR (CDCl₃, internal standard material: tetramethylsilane) ppm:1.46-1.48 (m, 3 H), 1.945-1.95 (s, 3 H), 3.38-3.39 (s, 3 H), 3.65-3.9(m, 4 H), 5.65-5.67 (w, 1 H), 6.02-6.07 (m, 1 H), 6.12-6.18 (w, 1 H)

[SYNTHESIS EXAMPLE 6]

Synthesis of Cyclohexyloxyethyl Methacrylate represented with theformula [11] ##STR12##

In the same way as the synthesis example 1, synthesis of monomer wasperformed using 26.5 grams (0.21 mols) of cyclohexylvinylether in placeof ethylvinylether. As a result, there was obtained 42.3 grams ofcyclohexyloxyethyl methacrylate. The yield was 95%.

IR (liquid film method) (cm⁻¹): 2950, 2880 (ν_(C--H)), 1720 (ν_(C)═O),1640 (ν_(C)═C), 1170 (ν_(C--O))

¹ H-NMR (CDCl₃, internal standard material: tetramethylsilane) ppm:1.41-1.5 (s, 13 H), 1.9-1.94 (s, 3 H), 3.47-3.53 (s, 1 H), 5.59-5.69 (w,1 H), 6.02-6.07 (s, 1 H), 6.15-6.25 (w, 1 H)

[SYNTHESIS EXAMPLE 7]

Synthesis of Acetoxyethoxyethyl Methacrylate represented with theformula [12] ##STR13##

Followings were put into 500 ml flask having four inlets and equippedwith a calcium chloride (CaCl₂) drying tube, an isotactic droppingfunnel and a thermometer:

(a) 23.5 grams (0.3 mols) of 2-chloroethylvinylehter;

(b) 18.9 grams (0.23 mols) of sodium acetate anhydride; and

(c) 0.5 grams (0.0014 mols) of tetrabutylammoniumchloride.

The mixture of (a) to (c) was refluxed with being stirred and heated for12 hours. Then, the resultant mixture was cooled down to roomtemperature, and solid constituents were removed by filtering. Then, theresultant mixture was distilled under reduced pressure. As a result,there was obtained 26.6 grams of acetoxyethylvinylehter. The yield was87%.

The thus obtained acetoxyethylvinylether by 19.5 grams (0.15 mols) andmethacrylic acid by 15.5 grams (0.18 mols) were dissolved into methylenechloride. Then, 0.38 grams (0.0015 mols) of p-toluenesulfonic acidpyridine salt was added into the mixture, and stirred for completedissolution. The resultant mixture is stood at room temperature for 6hours. Then, the mixture was washed three times with 2.5% aqueous sodiumhydroxide, and six times with water. Then, the resultant mixture wasdehydrated with magnesium sulfate. After filtering magnesium sulfateout, solvent was removed by means of an evaporator. Then, the resultantresidue was distilled under reduced pressure, thereby there was obtained29.6 grams of acetoxyethoxyethylvinylether (b.p. 100-105° C./0.07 mmHg).The yield was 93%.

IR (liquid film method) (cm⁻¹): 2950, 2880 (ν_(C--H)), 1720 (ν_(C)═O),1640 (ν_(C)═C), 1170 (ν_(C--O))

¹ H-NMR (CDCl₃, internal standard material: tetramethylsilane) ppm:1.945-1.95 (s, 3 H), 2.06-1.08 (s, 3 H), 3.82-3.85 (t, 2 H), 4.2-4.28(t, 2 H), 5.64-5.67 (s, 1 H), 6.02-6.07 (m, 1 H), 6.12-6.18 (s, 1 H)

[SYNTHESIS EXAMPLE 8]

Synthesis of Ethoxyethoxyethyl Methacrylate represented with the formula[13] ##STR14##

In the same way as the synthesis example 7, synthesis of monomer wasperformed using 15.6 grams (0.23 mols) of sodium ethanol salt in placeof sodium acetate salt. As a result, there was obtained 26.4 grams ofethoxyethoxyethyl methacrylate. The yield was 88%.

IR (liquid film method) (cm⁻¹): 2950, 2880 (ν_(C--H)), 1720 (ν_(C)═O),1640 (ν_(C)═C), 1170 (ν_(C--O))

¹ H-NMR (CDCl₃, internal standard material: tetramethylsilane) ppm:1.1-1.3 (s, 3 H), 1.4-1.5 (s, 3 H), 1.945-1.95 (s, 3 H), 3.5-3.95 (t, 6H), 5.64-5.67 (s, 1 H), 6.02-6.07 (m, 1 H), 6.12-6.18 (s, 1 H)

[SYNTHESIS EXAMPLE 9]

Synthesis of Buthoxyethoxyethyl Methacrylate represented with theformula [14] ##STR15##

In the same way as the synthesis example 7, synthesis of monomer wasperformed using 40.3 grams (0.23 mols) of sodium buthanol salt in placeof sodium acetate salt. As a result, there was obtained 41.7 grams ofbuthoxyethoxyethyl methacrylate. The yield was 90%.

IR (liquid film method) (cm⁻¹): 2950, 2880 (ν_(C--H)), 1720 (ν_(C)═O),1640 (ν_(C)═C), 1170 (ν_(C--O))

¹ H-NMR (CDCl₃, internal standard material: tetramethylsilane) ppm:1.05-2.2 (m, 21 H), 3.82-3.85 (t, 2 H), 4.2-4.28 (t, 2 H), 5.64-5.67 (s,1 H), 6.02-6.07 (m, 1 H), 6.12-6.18 (s, 1 H)

[SYNTHESIS EXAMPLE 10]

Synthesis of Propylcarbonyloxyethoxyethyl Methacrylate represented withthe formula [15] ##STR16##

In the same way as the synthesis example 6, synthesis of monomer wasperformed using 25.3 grams (0.23 mols) of sodium butyrate salt in placeof sodium acetate salt. As a result, there was obtained 32 grams ofpropylcarbonyloxyethoxyethyl methacrylate. The yield was 89%.

IR (liquid film method) (cm⁻¹): 2950, 2880 (ν_(C--H)), 1720 (ν_(C)═O),1640 (ν_(C)═C), 1170 (ν_(C--O))

¹ H-NMR (CDCl₃, internal standard material: tetramethylsilane) ppm:0.98-1.2 (t, 3 H), 1.5-1.95 (t, 3 H), 1.945-1.95 (s, 3 H), 2.06-2.08 (s,3 H), 3.82-3.85 (t, 2 H), 4.2-4.28 (t, 2 H), 5.64-5.67 (s, 1 H),6.02-6.07 (m, 1 H), 6.12-6.18 (s, 1 H)

[SYNTHESIS EXAMPLE 11]

Synthesis of Adamantyloxyethoxyethyl Methacrylate represented with theformula [16] ##STR17##

In the same way as the synthesis example 6, synthesis of monomer wasperformed using 40.3 grams (0.23 mols) of sodium 1-damantylalcohol saltin place of sodium acetate salt. As a result, there was obtained 41.7grams of adamantyloxyethoxyethyl methacrylate. The yield was 90%.

IR (liquid film method) (cm⁻¹): 2950, 2880 (ν_(C--H)), 1720 (ν_(C)═O),1640 (ν_(C)═C), 1170 (ν_(C--O))

¹ H-NMR (CDCl₃, internal standard material: tetramethylsilane) ppm:1.05-2.2 (m, 21 H), 3.82-3.85 (t, 2 H), 4.2-4.28 (t, 2 H), 5.64-5.67 (s,1 H), 6.02-6.07 (m, 1 H), 6.12-6.18 (s, 1 H)

[SYNTHESIS EXAMPLE 12]

Synthesis of Adamantylcarbonyloxyethoxyethyl Methacrylate representedwith the formula [17] ##STR18##

In the same way as the synthesis example 6, synthesis of monomer wasperformed using 46.7 grams (0.23 mols) of sodium 1-damantylcarboxylicacid salt in place of sodium acetate salt. As a result, there wasobtained 46.5 grams of adamantylcarbonyloxyethoxyethyl methacrylate. Theyield was 92%.

IR (liquid film method) (cm⁻¹): 2950, 2880 (ν_(C--H)), 1720 (ν_(C)═O),1640 (ν_(C)═C), 1170 (ν_(C--O))

¹ H-NMR (CDCl₃, internal standard material: tetramethylsilane) ppm:1.05-2.2 (m, 22 H), 3.82-3.85 (t, 2 H), 4.2-4.28 (t, 2 H), 5.64-5.67 (w,1 H), 6.02-6.07 (m, 1 H), 6.12-6.18 (w, 1 H)

[EMBODIMENT 1]

Synthesis of Poly (tricyclodecylacrylate-ethoxyethylmethacrylate-methacrylic acid) represented with the formula [18](Composition Ratio=5:3:2) ##STR19##

Following (a) to (c) were disclosed in 80 grams of dry tetrahydrofuranunder argon (Ar) gas atmosphere within a 300-ml egg plant shaped flaskhaving a three way type plug.

(a) 21.7 grams (0.105 mols) of tricyclodecylacrylate commerciallyavailable from Hitachi Kasei Co. Ltd. under the tradename "FA-513A".

(b) 10 grams (0.063 mols) of ethoxyethyl methacrylate which is acompound having been obtained in the synthesis example 1.

(c) 3.63 grams (0.042 mols) of methacrylic acid.

The composition ratio among the materials (a) to (c) was 5:3:2. Then, 30ml solution of tetrahydrofuran in which 1.5 grams (0.00915 mols) ofazobisisobutyronitrile, which is one of polymerization initiators, wasdissolved was added to the mixture of (a) to (c). Then, the resultantmixture was heated at 60-65° C. for an hour. Then, reprecipitation wasrepeated twice by introducing the resultant solution into 1 liter ofligroin. Precipitated polymer was collected by filtering, and dried at 2mmHg at 40° C. for 24 hours under reduced pressure. As a result, therewas obtained 20.2 grams ofpoly(tricyclodecylacrylate-ethoxyethylmethacrylate-methacrylic acid) inthe form of white powder. The yield was 57%. The copolymerization ratioobtained by ¹ H-NMR measurement was almost the same as the compositionratio among the above listed materials (a) to (c). The polystyreneequivalent weight-average molecular weight was 29,600, and the degree ofdispersion was 2.17.

IR (KBr briquette method) (cm⁻¹): 2400-3500 (ν_(O--H)), 2950, 2880(ν_(C--H)), 1722 (ν_(C)═O), 1660 (ν_(C)═O), 1170 (ν_(C--O))

[EMBODIMENT 2]

Synthesis of Poly (tricyclodecylacrylate-buthoxyethylmethacrylate-methacrylic acid) represented with the formula [19](Composition Ratio=5:3:2) ##STR20##

In the same way as the embodiment 1, synthesis of terpolymer wasperformed using 11.7 grams (0.0632 mols) of buthoxyethyl methacrylate,which is a compound having been obtained in the synthesis example 2, inplace of ethoxyethyl methacrylate. As a result, there was obtained 20.5grams of poly (tricyclodecylacrylate-buthoxyethylmethacrylate-methacrylic acid) in the form of white powder. The yieldwas 55%.

Weight-Average Molecular Weight (polystyrene equivalent molecularweight)=27,600, Degree of Dispersion=2.29

IR (cm⁻¹): 2400-3500 (ν_(O--H)), 2950, 2880 (ν_(C--H)), 1722 (ν_(C)═O),1660 (ν_(C)═O), 1170 (ν_(C--O))

[EMBODIMENT 3]

Synthesis of Poly (tricyclodecylacrylate-octyloxyethylmethacrylate-methacrylic acid) represented with the formula [20](Composition Ratio=5:3:2) ##STR21##

In the same way as the embodiment 1, synthesis of terpolymer wasperformed using 16.8 grams (0.0632 mols) of octyloxyethyl methacrylate,which is a compound having been obtained in the synthesis example 3, inplace of ethoxyethyl methacrylate. As a result, there was obtained 20grams of poly (tricyclodecylacrylate-octyloxyethylmethacrylate-methacrylic acid) in the form of white powder. The yieldwas 48%.

Weight-Average Molecular Weight (polystyrene equivalent molecularweight)=27,600, Degree of Dispersion=2.44

IR (cm⁻¹): 2400-3500 (ν_(O--H)), 2950, 2880 (ν_(C--H)), 1722 (ν_(C)═O),1660 (ν_(C)═O), 1170 (ν_(C--O))

[EMBODIMENT 4]

Synthesis of Poly (tricyclodecylacrylate-methoxypropylmethacrylate-methacrylic acid) represented with the formula [21](Composition Ratio=5:3:2) ##STR22##

In the same way as the embodiment 1, synthesis of terpolymer wasperformed using 10 grams (0.0632 mols) of methoxypropyl methacrylate,which is a compound having been obtained in the synthesis example 4, inplace of ethoxyethyl methacrylate. As a result, there was obtained 17.6grams of poly (tricyclodecylacrylate-methoxypropylmethacrylate-methacrylic acid) in the form of white powder. The yieldwas 50%.

Weight-Average Molecular Weight (polystyrene equivalent molecularweight)=27,600, Degree of Dispersion=2.41

IR (cm⁻¹): 2400-3500 (ν_(O--H)), 2950, 2880 (ν_(C--H)), 1722 (ν_(C)═O),1660 (ν_(C)═O), 1170 (ν_(C--O))

[EMBODIMENT 5]

Synthesis of Poly (tricyclodecylacrylate-methoxyethoxyethylmethacrylate-methacrylic acid) represented with the formula [22](Composition Ratio=5:3:2) ##STR23##

In the same way as the embodiment 1, synthesis of terpolymer wasperformed using 11.9 grams (0.0632 mols) of methoxyethoxyethylmethacrylate, which is a compound having been obtained in the synthesisexample 5, in place of ethoxyethyl methacrylate. As a result, there wasobtained 19.1 grams of poly (tricyclodecylacrylate-methoxyethoxyethylmethacrylate-methacrylic acid). The yield was 52%.

Weight-Average Molecular Weight (polystyrene equivalent molecularweight)=28,800, Degree of Dispersion=2.41

IR (cm⁻¹): 2400-3500 (ν_(O--H)), 2950, 2880 (ν_(C--H)), 1722 (ν_(C)═O),1660 (ν_(C)═O), 1170 (ν_(C--O))

[EMBODIMENT 6]

Synthesis of Poly (tricyclodecylacrylate-cyclohexylethylmethacrylate-methacrylic acid) represented with the formula [23](Composition Ratio=5:3:2) ##STR24##

In the same way as the embodiment 1, synthesis of terpolymer wasperformed using 13.4 grams (0.0632 mols) of cyclohexylethylmethacrylate, which is a compound having been obtained in the synthesisexample 6, in place of ethoxyethyl methacrylate. As a result, there wasobtained 19.7 grams of poly (tricyclodecylacrylate-cyclohexylethylmethacrylate-methacrylic acid). The yield was 51%.

Weight-Average Molecular Weight (polystyrene equivalent molecularweight)=26,600, Degree of Dispersion=2.2

IR (cm⁻¹): 2400-3500 (ν_(O--H)), 2950, 2880 (ν_(C--H)), 1722 (ν_(C)═O),1660 (ν_(C)═O), 1170 (ν_(C--O))

[EMBODIMENT 7]

Synthesis of Poly (tricyclodecylacrylate-acetoxyethoxyethylmethacrylate-methacrylic acid) represented with the formula [24](Composition Ratio=5:3:2) ##STR25##

In the same way as the embodiment 1, synthesis of terpolymer wasperformed using 14 grams (0.0632 mols) of acetoxyethoxyethylmethacrylate, which is a compound having been obtained in the synthesisexample 7, in place of ethoxyethyl methacrylate. As a result, there wasobtained 20 grams of poly (tricyclodecylacrylate-acetoxyethoxyethylmethacrylate-methacrylic acid). The yield was 51%.

Weight-Average Molecular Weight (polystyrene equivalent molecularweight)=21,000, Degree of Dispersion=2.25

IR (cm⁻¹): 2400-3500 (ν_(O--H)), 2950, 2880 (ν_(C--H)), 1722 (ν_(C)═O),1660 (ν_(C)═O), 1170 (ν_(C--O))

[EMBODIMENT 8]

Synthesis of Poly (tricyclodecylacrylate-ethoxyethoxyethylmethacrylate-methacrylic acid) represented with the formula [25](Composition Ratio=5:3:2) ##STR26##

In the same way as the embodiment 1, synthesis of terpolymer wasperformed using 14.5 grams (0.0632 mols) of ethoxyethoxyethylmethacrylate, which is a compound having been obtained in the synthesisexample 8, in place of ethoxyethyl methacrylate. As a result, there wasobtained 19.1 grams of poly (tricyclodecylacrylate-ethoxyethoxyethylmethacrylate-methacrylic acid). The yield was 51%.

Weight-Average Molecular Weight (polystyrene equivalent molecularweight)=26,600, Degree of Dispersion=2.2

IR (cm⁻¹): 2400-3500 (ν_(O--H)), 2950, 2880 (ν_(C--H)), 1722 (ν_(C)═O),1660 (ν_(C)═O), 1170 (ν_(C--O))

[EMBODIMENT 9]

Synthesis of Poly (tricyclodecylacrylate-buthoxyethoxyethylmethacrylate-methacrylic acid) represented with the formula [26](Composition Ratio=5:3:2) ##STR27##

In the same way as the embodiment 1, synthesis of terpolymer wasperformed using 19.3 grams (0.0636 mols) of buthoxyethoxyethylmethacrylate, which is a compound having been obtained in the synthesisexample 9, in place of ethoxyethyl methacrylate. As a result, there wasobtained 21.9 grams of poly (tricyclodecylacrylate-buthoxyethoxyethylmethacrylate-methacrylic acid). The yield was 55%.

Weight-Average Molecular Weight (polystyrene equivalent molecularweight)=26,600, Degree of Dispersion=2.2

IR (cm⁻¹): 2400-3500 (ν_(O--H)) 2950, 2880 (ν_(C--H)), 1722 (ν_(C)═O),1660 (ν_(C)═O), 1170 (ν_(C--O))

[EMBODIMENT 10]

Synthesis of Poly (tricyclodecylacrylate-propylcarbonyloxyethoxyethylmethacrylate-methacrylic acid) represented with the formula [27](Composition Ratio=4:4:2) ##STR28##

In the same way as the embodiment 1, synthesis of terpolymer wasperformed using 3.4 grams (0.0166 mols) of tricyclodecanylacrylate, 0.7grams (0.0083 mols) of methacrylic acid, and 4 grams (0.0166 mols) ofpropylcarbonyloxyethoxyethyl methacrylate, which is a compound havingbeen obtained in the synthesis example 10, in place of ethoxyethylmethacrylate. As a result, there was obtained 4.86 grams of poly(tricyclodecylacrylate-propylcarbonyloxyethoxyethylmethacrylate-methacrylic acid). The yield was 60%.

Weight-Average Molecular Weight (polystyrene equivalent molecularweight)=27,600, Degree of Dispersion=2.29

IR (cm⁻¹): 2400-3500 (ν_(O--H)), 2950, 2880 (ν_(C--H)), 1722 (ν_(C)═O),1660 (ν_(C)═O), 1170 (ν_(C--O))

[EMBODIMENT 11]

Synthesis of Poly (tricyclodecylacrylate-adamantyloxyethoxyethylmethacrylate-methacrylic acid) represented with the formula [28](Composition Ratio=4:4:2) ##STR29##

In the same way as the embodiment 1, synthesis of terpolymer wasperformed using 3.4 grams (0.0166 mols) of tricyclodecanylacrylate, 0.7grams (0.0083 mols) of methacrylic acid, and 5 grams (0.0166 mols) ofadamantyloxyethoxyethyl methacrylate, which is a compound having beenobtained in the synthesis example 7, in place of ethoxyethylmethacrylate. As a result, there was obtained 5.4 grams of poly(tricyclodecylacrylate-adamantyloxyethoxyethyl methacrylate-methacrylicacid). The yield was 60%.

Weight-Average Molecular Weight (polystyrene equivalent molecularweight)=29,500, Degree of Dispersion=2.35

IR (cm⁻¹): 2400-3500 (ν_(O--H)), 2950, 2880 (ν_(C--H)), 1722 (ν_(C)═O),1660 (ν_(C)═O), 1170 (ν_(C--O))

[EMBODIMENT 12]

Synthesis of Poly (tricyclodecylacrylate-adamantylcarbonyloxyethoxymethacrylate-methacrylic acid) represented with the formula [29](Composition Ratio=5:3:2) ##STR30##

In the same way as the embodiment 1, synthesis of terpolymer wasperformed using 19.3 grams (0.0636 mols) ofadamantylcarbonyloxyethoxyethyl methacrylate, which is a compound havingbeen obtained in the synthesis example 8, in place of ethoxyethylmethacrylate. As a result, there was obtained 24 grams of poly(tricyclodecylacrylate-adamantylcarbonyloxyethoxyethylmethacrylate-methacrylic acid). The yield was 55%.

Weight-Average Molecular Weight (polystyrene equivalent molecularweight)=26,600, Degree of Dispersion=2.2

IR (cm⁻¹): 2400-3500 (ν_(O--H)), 2950, 2880 (ν_(C--H)), 1722 (ν_(C)═O),1660 (ν_(C)═O), 1170 (ν_(C--O))

[EMBODIMENT 13]

Thermal decomposition points were measured by means of a differentialthermal decomposition apparatus with respect to the polymers obtained inthe embodiments 1 to 12 and the polymer obtained in the synthesisexample 1, which is protected with a tetrahydropyranyl group. Theresults were shown in Table 1. Herein, the thermal decomposition point(referred to simply as "TDP" in Table 1) is defined as a temperature atwhich a weight of a polymer is decreased by 5%.

                  TABLE 1                                                         ______________________________________                                        Polymer              TDP                                                      ______________________________________                                        Polymer of Embodiment 1                                                                            158° C.                                             Polymer of Embodiment 2 160° C.                                        Polymer of Embodiment 3 171° C.                                        Polymer of Embodiment 4 144° C.                                        Polymer of Embodiment 5 174° C.                                        Polymer of Embodiment 6 139° C.                                        Polymer of Embodiment 7 173° C.                                        Polymer of Embodiment 8 174° C.                                        Polymer of Embodiment 9 172° C.                                        Polymer of Embodiment 10 178° C.                                       Polymer of Embodiment 11 196° C.                                       Polymer of Embodiment 12 205° C.                                       Polymer of Reference Example 1 134° C.                               ______________________________________                                    

[EMBODIMENT 14]

There was prepared a resist composed of the following materials A, B andC. The experiment mentioned hereinbelow was conducted under a yellowlamp.

(A) 0.99 grams of poly (tricyclodecanylacrylate-ethoxyethylmethacrylate-methacrylic acid), which is the polymer having beensynthesized in the embodiment 1. The copolymerization ratio was 5:3:2.

(B) 0.01 gram of N-hydroxysuccinimidetoluenesulfonate (photo acidgenerator)

(C) 4.000 grams of propyleneglycolmonomethylether acetate (solvent)

The mixture composed of the above mentioned materials A, B and C wasfiltrated with a 0.2 μm teflon filter to thereby prepare a resist. Thethus prepared resist was applied on a 3-inch thickness silicon wafer 1by spin coating process, and then heated at 90° C. for 60 seconds on ahot plate. Thus, there was formed a thin resist layer 2 having athickness of 0.5 μm on the wafer 1, as illustrated in FIG. 1. Then, asillustrated in FIG. 4, the wafer 1 on which the thin layer 2 was formedwas placed on an X-Y stage 7 in a light-radiating apparatus 8sufficiently purged with nitrogen. On the resist layer 2 was closelyplaced a mask 9 comprising a quartz plate 4 on which a pattern 3composed of chrome was formed, and then ArF excimer laser beam 5 wasirradiated to the resist layer 2 through a homogenizer 10 and furtherthrough the mask 9, as illustrated in FIGS. 2 and 4. Shortly after that,the wafer 1 was baked on a hot plate at 90° C. for 60 seconds, and thenwas developed by dipping in an alkaline developing reagent for 60seconds. The alkaline developing reagent is an aqueous solutioncontaining tetramethylammoniumhydroxide by 0.048%, and was maintained at23° C. Subsequently, the wafer 1 was rinsed in pure water for 60seconds. As a result, only exposed regions of the resist layer 2 wasdissolved and thus removed in the developing reagent, thereby there wasobtained a positive type pattern 2a, as illustrated in FIG. 3.

In this experiment, 0.20 μm line and space (L/S) resolution was obtainedwhen the exposure energy was approximately 30 mJ/cm². The pattern 2a wasresolved and observed with a scanning electron microscope (SEM)commercially available from Hitachi Co. Ltd,. under the tradename ofSE-4100 with the result that undeveloped regions and peel-off of thepattern were not observed.

[EMBODIMENTS 15-25]

In the same way as the embodiment 14, the same experiment was conductedusing the polymers obtained in the embodiments 2-12 in place of thepolymer obtained in the embodiment 1. In the embodiments 20 and 21,post-exposure heat treatment was carried out at 100° C. for 60 seconds.The resolution of the patterns and the associated exposure dose(referred to simply as "ED" in Table 2) are shown in Table 2. Thepattern was resolved and observed with SEM with the result thatundeveloped regions and peel-off of the pattern were not observed.

                  TABLE 2                                                         ______________________________________                                                              Resolution                                                                             ED                                               Polymer [μmL/S] [mJ/cm.sup.2 ]                                           ______________________________________                                        Embodiment 15                                                                           Polymer of Embodiment 2                                                                       0.2      30                                           Embodiment 16 Polymer of Embodiment 3 0.22 31                                 Embodiment 17 Polymer of Embodiment 4 0.22 25                                 Embodiment 18 Polymer of Embodiment 5 0.22 28                                 Embodiment 19 Polymer of Embodiment 6 0.25 25                                 Embodiment 20 Polymer of Embodiment 7 0.20 33                                 Embodiment 21 Polymer of Embodiment 8 0.20 35                                 Embodiment 22 Polymer of Embodiment 9 0.22 40                                 Embodiment 23 Polymer of Embodiment 10 0.25 33                                Embodiment 24 Polymer of Embodiment 11 0.25 50                                Embodiment 25 Polymer of Embodiment 12 0.25 32                              ______________________________________                                    

[REFERENCE EXAMPLE 1]

Synthesis of poly (tricyclodecanylacrylate-tetrahydropyranylmethacrylate-methacrylic acid) represented with the general formula [30]##STR31##

Followings (a) to (c) were dissolved in 80 grams of dry tetrahydrofuranunder argon (Ar) gas atmosphere within a 300-ml egg plant shaped flaskhaving a three way type plug.

(a) 14 grams (0.068 mols) of tricyclodecanylacrylate.

(b) 6.8 grams (0.04 mols) of tetrahydropyranyl methacrylate, which wassynthesized by a conventional method such as G. N. Taylor, ChemistryMaterial, Vol. 3 (6), 1991, pp. 1031-1040.

(c) 2.32 grams (0.027 mols) of methacrylic acid.

The composition ratio among the materials (a) to (c) was 5:3:2. Then, 30ml solution of tetrahydrofuran in which 1.55 grams (0.00915 mols) ofazobisisobutyronitrile, which is one of polymerization initiators, wasdissolved was added to the mixture of (a) to (c). Then, the resultantmixture was heated at 60-70° C. for an hour. Then, reprecipitation wasrepeated twice by introducing the resultant solution into 1 liter ofhexane. Precipitated polymer was collected by filtering, and dried at 2mmHg at 40° C. for 24 hours under reduced pressure. As a result, therewas obtained 14.0 grams ofpoly(tricyclodecanylacrylate-tetrahydropyranyl methacrylate-methacrylicacid) in the form of white powder. The yield was 60%. Thecopolymerization ratio obtained by ¹ H-NMR measurement was almost thesame as the composition ratio among the above listed materials (a) to(c). The polystyrene equivalent weight-average molecular weight was28,000, and the degree of dispersion was 2.28.

[REFERENCE EXAMPLE 2]

Synthesis of Poly (tricyclodecanylacrylate-tert-butylmethacrylate-methacrylic acid) represented with the formula [31]##STR32##

In the same way as the reference example 1, synthesis of poly(tricyclodecanylacrylate-tert-butyl methacrylate-methacrylic acid) wasperformed using 5.8 grams (0.04 mols) of tert-butyl methacrylate inplace of tetrahydro methacrylate. As a result, there was obtained 13.9grams of poly (tricyclodecanylacrylate-tert-butylmethacrylate-methacrylic acid) in the form of white powder. Thecopolymerization ratio was 5:3:2. The yield was 63%. The weight-averagemolecular weight was 28,000, and the degree of dispersion was 2.28.

[REFERENCE EXAMPLE 3]

There was prepared a resist composed of the following materials A, B andC. The experiment mentioned hereinbelow was conducted under a yellowlamp.

(A) 0.99 grams of the polymer synthesized in the reference example 1.

(B) 0.01 gram of N-hydroxysuccinimidetoluenesulfonate (photo acidgenerator)

(C) 4.000 grams of propyleneglycolmonomethylether acetate (solvent)

The mixture composed of the above mentioned materials A, B and C wasfiltrated with a 0.2 μm teflon filter to thereby prepare a resist. Thethus prepared resist was applied on a 3-inch thickness silicon substrateby spin coating process, and then baked at 90° C. for 60 seconds on ahot plate. Thus, there was formed a thin resist layer having a thicknessof 0.7 μm on the substrate. Then, the substrate on which the thin layerwas formed was placed in a light-radiating apparatus sufficiently purgedwith nitrogen. On the resist layer was closely placed a mask comprisinga quartz plate on which a pattern composed of chrome was formed, andthen ArF excimer laser beam was irradiated to the resist layer throughthe mask. Shortly after that, the substrate was baked on a hot plate at90° C. for 60 seconds, and then was developed by dipping in an alkalinedeveloping reagent for 60 seconds. The alkaline developing reagent is anaqueous solution containing tetramethylammoniumhydroxide by 0.048 weightpercent, and was maintained at 23° C. Subsequently, the wafer 1 wasrinsed in pure water for 60 seconds. As a result, only exposed regionsof the resist layer was dissolved and thus removed in the developingreagent, thereby there was obtained a positive type pattern.

In this experiment, 0.25 μm line and space (L/S) resolution was obtainedwhen the exposure energy was approximately 47.3 mJ/cm². However, therewas observed resist residue or unremoved resist portion.

[REFERENCE EXAMPLE 4]

There was prepared a resist composed of the following materials A, B andC. The experiment mentioned hereinbelow was conducted under a yellowlamp.

(A) 0.99 grams of the polymer synthesized in the reference example 2

(B) 0.01 gram of N-hydroxysuccinimidetoluenesulfonate (photo acidgenerator)

(C) 4.000 grams of propyleneglycolmonomethylether acetate (solvent)

The mixture composed of the above mentioned materials A, B and C wasfiltrated with a 0.2 μm teflon filter to thereby prepare a resist. Thethus prepared resist was applied on a 3-inch thickness silicon wafer byspin coating process, and then baked at 80° C. for 60 seconds on a hotplate. Thus, there was formed a thin resist layer having a thickness of0.7 μm on the wafer. Then, the wafer on which the thin layer was formedwas placed in a light-radiating apparatus sufficiently purged withnitrogen. On the resist layer was closely placed a mask comprising aquartz plate on which a pattern composed of chrome was formed, and thenArF excimer laser beam was irradiated to the resist layer through themask. Shortly after that, the substrate was baked on a hot plate at 110°C. for 60 seconds, and then was developed by dipping in an alkalinedeveloping reagent for 60 seconds. The alkaline developing reagent is anaqueous solution containing tetramethylammoniumhydroxide by 2.3 weightpercent, and was maintained at 23° C. Subsequently, the wafer 1 wasrinsed in pure water for 30 seconds. As a result, a fine resist patternwas not formed.

As having been described in connection with the preferred embodiments,the polymer made in accordance with the present invention is thermallystable, and has a high efficiency of decomposition by acid. Hence, thephotoresist containing the polymer can have high resolution, andaccordingly provides a fine pattern without production of scum.

While the present invention has been described in connection withcertain preferred embodiments, it is to be understood that the subjectmatter encompassed by way of the present invention is not to be limitedto those specific embodiments. On the contrary, it is intended for thesubject matter of the invention to include all alternatives,modifications and equivalents as can be included within the spirit andscope of the following claims.

What is claimed is:
 1. A photo resist comprising: a resin composed of apolymer represented with the following general formula (1); and a photoacid generator which produces acid when exposed to a light, said resinhas a weight percent in the range of 75 to 99.8 both inclusive, and saidphoto acid generator has a weight percent in the range of 0.2 to 25 bothinclusive: ##STR33## wherein each of R¹, R³, and R⁷ represents one of ahydrogen atom and a methyl group, R² represents a hydrocarbon group, R⁴represents one of a hydrogen atom and a hydrocarbon group having acarbon number of 1 or 2, R⁵ represents a hydrocarbon group having acarbon number of 1 or 2, R⁶ represents one of (a) a hydrocarbon grouphaving a carbon number in the range of 1 to 12, (b) a hydrocarbon grouphaving a carbon number in the range of 1 to 12 and replaced with analkoxy group having a carbon number in the range of 1 to 12, and (c) ahydrocarbon group having a carbon number in the range of 1 to 12 andreplaced with an acyl group having a carbon number in the range of 1 to13, x+y+z=1, x is in the range of 0.1 to 0.9, y is in the range of 0.1to 0.7, and z is in the range of 0 to 0.7.
 2. The photoresist as setforth in claim 1, wherein said polymer has a weight average molecularweight in the range of 1,000 to 1,000,000.
 3. The photoresist as setforth in claim 1, wherein said resin has a weight percent in the rangeof 85 to 99.5, and said photo acid generator has a weight percent in therange of 0.5 to
 15. 4. The photoresist as set forth in claim 1, whereinsaid photo acid generator is one represented by the following generalformula (3): ##STR34## wherein each of R⁷ and R⁸ represents one ofstraight-chain, branch-type and cyclic alkyl groups, and R⁹ representsone of (a) a straight-chain, branch-type or cyclic alkyl group, (b) a2-oxo cyclic alkyl group, (c) a 2-oxo straight chain alkyl group, an (d)a 2-oxo branch-type alkyl group, and Y⁻ represents a negative ion. 5.The photoresist as set forth in claim 1, wherein said photo acidgenerator is one represented with the following general formula (4):##STR35## wherein R¹⁰ represents one of (a) straight-chain, branch-typeor cyclic alkyl group, (b) a replaced aromatic ring, and (c) anon-replaced aromatic ring, and each of R¹¹ and R¹² represents one of(a) a straight-chain, branch-type or cyclic alkyl group and (b) astraight-chain, branch-type or cyclic haloalkyl group.
 6. A photo resistas in claim 1 wherein R² is a bridged cyclic hydrocarbon group andhaving a carbon number in the range of 7 to 13.